The setting reaction of ionomer cements is known mainly through studies of glass ionomer cements, i.e., ionomer cements in which the powder used in the cement is an ion-leachable glass, such as those based on calcium aluminosilicate glasses, or more recently, borate glasses. See generally, Prosser et al., "Polyelectrolyte Cements", Wilson and Prosser, eds., Developments in Ionic Polymers-1, Chapter 5, Applied Science Publishers (London and New York, 1983). In the setting reaction, the powder behaves like a base and reacts with the acidic polyelectrolyte, i.e., ionomer, to form a metal polysalt which acts as the binding matrix. Water serves as a reaction medium and allows the transport of ions in what is essentially an ionic reaction.
The setting reaction is therefore characterized as a chemical cure system that proceeds automatically upon mixing the ionomer and powder in the presence of water. The cements set to a gel-like state within a few minutes and rapidly harden to develop strength. See, e.g., Prosser et al., J. Chem. Tech. Biotechnol., 29, 69-87 (1979). Chelating agents, such as tartaric acid, have been described as useful for modifying the rate of setting, e.g., to provide longer working times for the cements. See, e.g., U.S. Pat. Nos. 4,089,830, 4,209,434, 4,317,681 and 4,374,936. Unfortunately, when working times are lengthened by the usual methods, setting times are generally also lengthened.
Many commercially available glass ionomer cements include such chelating agents, and as a result are characterized by working times that are on the order of 1 to 2 minutes, but relatively long setting times, e.g., on the order of 4 to 15 minutes. During this set time a dry field must be maintained, and yet dessication of the cement must be avoided. Such conditions can lead to discomfort for the patient as well as the added burden of having to spend extra time in the dentist's chair. Thus present day glass ionomer cements, although beneficial clinically, are quite technique-sensitive, as well as time-consuming for the dentist and patient.
Of peripheral relevance to the present invention, but worth noting nonetheless, Mathis et al., J. Dent. Res., 66:113 (Abst. No. 51) (1987), reports the addition of a separate light curable composite resin to the liquid component of an ionomer in order to form a "hybrid" material. This hybrid material was cured by exposure to a visible light source immediately after mixing it with powder.